Autoimmune diseases are characterized by an abnormal immune response directed against normal autologous (self) tissues.
Based on the type of immune response (or immune reaction) involved, autoimmune diseases in mammals can generally be classified in one of two different categories: cell-mediated (i.e., T-cell-mediated) or antibody-mediated (i.e., .beta.-cell mediated) disorders. Non-limiting examples of T-cell-mediated autoimmune diseases include multiple sclerosis (MS), rheumatoid arthritis (RA), the autoimmune stage of diabetes mellitus (juvenile-onset or Type 1 diabetes) and autoimmune uveoretinitis (AUR). Antibody-mediated autoimmune diseases include without limitation myasthenia gravis (MG), autoimmune thyroiditis (AT), and systemic lupus erythematosus (SLE).
Both categories of autoimmune diseases are currently being treated with drugs that suppress immune responses systemically in a non-specific manner, i.e., drugs incapable of selectively suppressing the abnormal immune response. One such drug is methotrexate, a biological response modifier that selectively inhibits fast growing cells. However, methotrexate has significant toxic and other side effects and eventually induces "global" immunosuppression in the subject being treated. In other words, prolonged treatment with a normal course of methotrexate downregulates the normal protective immune response against pathogens, thereby increasing the risk of infection. In addition, patients subjected to prolonged global immunosuppression have an increased risk of developing severe medical complications from the treatment, such as malignancies, liver, and kidney failure.
To treat autoimmune disease, methotrexate is normally administered once a week in a high dose of, e.g., 7.5 to 25 mg. Such treatment is commonly used to treat rheumatoid arthritis, and has been effectively used to treat multiple sclerosis (Goodkin et al., Ann. Neurology. 37:30, 1995). Although oral administration is most common, methotrexate is also commercially available for parenteral administration for such treatment.
Recently, new methods and pharmaceutical formulations have been found that are useful for treating autoimmune diseases (and related T-cell mediated inflammatory disorders such as allograft rejection and retroviral-associated neurological disease). These treatments induce tolerance, orally or mucosally, e.g. by inhalation, using as tolerizers autoantigens, bystander antigens, or disease-suppressive fragments or analogs of autoantigens or bystander antigens. Such treatments are described in PCT Patent Applications Nos. PCT/US93/01705 filed Feb. 25, 1993, PCT/US91/01466 filed Mar. 4, 1991, PCT/US90/07455 filed Dec. 17, 1990, PCT/US90/03989 filed Jul. 16, 1990, PCT/US91/07475 filed Oct. 10, 1991, PCT/US93/07786 filed Aug. 17, 1993, PCT/US93/09113 filed Sep. 24, 1993, PCT/US91/08143 filed Oct. 31, 1991, PCT/US91/02218 filed Mar. 29, 1991, PCT/US93/03708 filed Apr. 20, 1993, PCT/US93/03369 filed Apr. 9, 1993, and PCT/US91/07542 filed Oct. 15, 1991. Autoantigens and bystander antigens are defined below.
Intravenous administration of autoantigens (and fragments thereof containing immunodominant epitopic regions of their molecules) has been found to induce immune suppression through a mechanism called clonal anergy. Clonal anergy causes deactivation of only immune attack T-cells specific to a particular antigen, the result being a significant reduction in the immune response to this antigen. Thus, the autoimmune response-promoting T-cells specific to an autoantigen, once anergized, no longer proliferate in response to that antigen. This reduction in proliferation also reduces the immune reactions responsible for autoimmune disease symptoms (such as neural tissue damage that is observed in MS). There is also evidence that oral administration of autoantigens (or immunodominant fragments) in a single dose and in substantially larger amounts than those that trigger "active suppression" may also induce tolerance through anergy (or clonal deletion).
A method of treatment has also been disclosed that proceeds by active suppression. Active suppression functions via a different mechanism from that of clonal anergy. This method, discussed extensively in PCT Application PCT/US93/01705, involves oral or mucosal administration of antigens specific to the tissue under autoimmune attack. These are called "bystander antigens" and are defined below. This treatment causes regulatory (suppressor) T-cells to be induced in the gut-associated lymphoid tissue (GALT), or bronchial associated lymphoid tissue (BALT), or most generally, mucosa associated lymphoid tissue (MALT) (MALT includes GALT and BALT). These regulatory cells are released in the blood or lymphatic tissue and then migrate to the organ or tissue afflicted by the autoimmune disease and suppress autoimmune attack of the afflicted organ or tissue. The T-cells elicited by the bystander antigen (which recognize at least one antigenic determinant of the bystander antigen used to elicit them) are targeted to the locus of autoimmune attack where they mediate the local release of certain immunomodulatory factors and cytokines, such as transforming growth factor beta (TGF-.beta.), interleukin-4 (IL-4), and/or interleukin-10 (IL-10). Of these, TGF-.beta. is an antigen-nonspecific immunosuppressive factor in that it suppresses immune attack regardless of the antigen that triggers the attack. (However, because oral or mucosal tolerization with a bystander antigen only causes the release of TGF-.beta. in the vicinity of autoimmune attack, no systemic immunosuppression ensues.) IL-4 and IL-10 are also antigen-nonspecific immunoregulatory cytokines. IL-4 in particular enhances Th2 response, i.e., acts on T-cell precursors and causes them to differentiate preferentially into Th2 cells at the expense of Th1 responses. IL-4 also indirectly inhibits Th1 exacerbation. IL-10 is a direct inhibitor of Th1 responses. After orally tolerizing mammals afflicted with autoimmune disease conditions with bystander antigens, increased levels of TGF-.beta., IL-4 and IL-10 are observed at the locus of autoimmune attack. Chen, Y. et al., Science, 265:1237-1240, 1994. The bystander suppression mechanism has been confirmed by von Herreth et al., J. Clin. Invest., 96:1324-1331, September 1996.
It has also been disclosed that oral or parenteral administration of Type I interferon, or polypeptides having Type I interferon activity, either alone or in conjunction with oral or mucosal administration of autoantigens or bystander antigens, is beneficial in reducing the symptoms of autoimmune disease. Suboptimal doses of Type I (.alpha. or .beta.) interferon potentiate the tolerizing effect of the autoantigens and bystander antigen. This work has been described in more detail in PCT application no. PCT/US95/04120, filed Apr. 07, 1995. Type I interferon, especially .beta.-IFN, is known to have certain immunomodulatory properties, e.g., inhibition of the activity of .gamma.-interferon (IFN-.gamma.). IFN-.gamma. has been shown to exacerbate MS, and may be involved in the pathogenesis of MS lesions. Thus, IFN-.beta. appears to have a beneficial effect due in part to its ability to inhibit IFN-.gamma. expression by T-cells.
PCT/US95/04512, filed Apr. 07, 1995, describes use of Th2-enhancing cytokines in conjunction with oral tolerization employing autoantigens or bystanders antigens.
None of these applications, however, describes any form of tolerization in combination with methotrexate therapy. Also, prior to the present invention, it was not known whether methotrexate, which inhibits cell division, would inhibit cells involved in mediating mucosal tolerance in the treatment of autoimmune disease.
One object of the invention is to allow administration of less toxic amounts of methotrexate in the treatment of autoimmune diseases.
An additional object is to allow administration of methotrexate in more frequent administrations in order to reduce the amount that is administered at one time.
Another object is to provide a treatment for autoimmune disease that is more effective than either administration of methotrexate alone or administration of an oral, or more generally, a mucosal tolerizing agent alone.